1. Field of the Invention
This invention relates to bobbin assemblies for supplies of thread as used on different sewing machines and, more particularly, to a bobbin assembly having structure which cooperates with a support for the bobbin assembly to prevent backlash of thread due to overrunning.
2. Background Art
Bobbins are used for thread supplies on a wide range of sewing equipment. Typically, the bobbin has a core with a rotational axis and axially spaced flanges which bound a storage space for thread wrapped around the core. The bobbin is mounted on a support for rotation around the core axis. By rotating the bobbin, thread wrapped around the core is controllably paid out.
Ideally, the bobbin is guidingly rotated during operation without any significant resistance as might cause uneven line distribution or, in a worse case, jamming of the bobbin. While smooth rotation of the bobbin is desirable during sewing operations, the unimpeded rotation of the bobbin potentially causes thread backlash. Ideally, as the machinery is stopped, the bobbin rotation simultaneously ceases. However, due to the free rotation of the bobbin, the momentum of the rotating bobbin causes it to continue to rotate which could produce a backlash in the thread. This may require that the machinery be shut down to allow the backlash to be eliminated. Severely backlashed thread may have to be cut. Potentially, there is a significant loss of operating time, as well as the inconvenience of having to manually remedy the backlash situation. Severe backlashing may require replacement of the bobbin with a bobbin having a new supply of thread. Consequently, significant amounts of thread may be wasted.
Potentially of greater significance is the fact that a slackened thread resulting from overrunning of the bobbin may cause at least temporary defective stitching after the equipment is re-started. This may lead to defective product that may have to either be re-stitched or destroyed.
To address this problem, it is known to install disk-like spring elements on a case which confines the bobbin into its operative position. These springs have deflectable arms which produce a frictional bias force on the bobbin. This force is preferably controlled so that it does not significantly impede rotation of the bobbin during a sewing operation yet produces enough resistance that the bobbin will not continue to rotate once the equipment is stopped, as might cause thread backlash.
In one form, the invention is directed to the combination of a bobbin assembly and a support for the bobbin assembly. The bobbin assembly has a core around which a supply of thread can be wrapped and having a rotational axis, a first flange having first and second oppositely facing surfaces with the first surface bounding a storage space for thread wrapped around the core, and a magnetic element. The support has a third surface with a first metal material facing the second surface with the bobbin assembly operatively connected to the support and sufficiently close to the magnetic element so that a magnetic field is created between the magnetic element and first metal material that tends to resist movement of the bobbin assembly relative to the support around the rotational axis of the core.
In one form, the first metal material is attracted to the magnetic element with a force that tends to resist movement of the bobbin assembly relative to the support means around the rotational axis of the core.
In one form, the magnetic element is a first discrete element on the first flange.
In one form, the first flange is made from a non-metallic material to which the first discrete element is attached.
The non-metallic material may be a moldable material, such as plastic.
In one form, the third surface is defined by a second material that is different than the first metal material.
A second magnetic element may additionally be provided on the first flange.
The invention is also directed to the combination of a bobbin assembly and a support for the bobbin assembly. The bobbin assembly has a core around which a supply of thread can be wrapped and having a rotational axis, and a first flange having first and second oppositely facing surfaces, with the first surface bounding a storage space for thread wrapped around the core. The first flange is made of a first metal material. The support has a third surface facing the second surface with the bobbin assembly operatively connected to the support and a magnetic element that is one of at or adjacent to the third surface so that a magnetic field is created between the magnetic element and first metal material that tends to resist movement of the bobbin assembly relative to the support around the rotational axis of the core.
The first metal material defines at least a part of the second surface.
The first metal material may be embedded in the first flange.
In one form, the first metal material is attracted to the magnetic element with a force that tends to resist movement of the bobbin assembly relative to the support around the rotational axis of the core.
The magnetic element may be a discrete element embedded in the support.
The invention is also directed to the combination of a bobbin assembly and a support for the bobbin assembly. The bobbin assembly has a core around which a supply of thread can be wrapped and having a central axis, a first flange having first and second oppositely facing surfaces with the first surface bounding a storage space with thread wrapped around the core, and a first magnetic element. A support has a third surface facing the second surface with the bobbin assembly operatively connected to the support and a second magnetic element that is one of at or adjacent to the third surface. The first and second magnetic elements interact to produce a force that tends to resist movement of the bobbin assembly relative to the support around the rotational axis of the core.
The force produced by the interaction of the first and second magnetic elements may be either an attractive force or a repulsive force.
The combination may further include a third magnetic element on the bobbin assembly that interacts with the second magnetic element to produce a force that tends to resist movement of the bobbin assembly relative to the support around the rotational axis of the core.
A third magnetic element may be provided on the support to interact with the first magnetic element to produce a force that tends to resist movement of the bobbin assembly relative to the support around the rotational axis of the core.
The third magnetic element may be embedded in moldable material.
The first magnetic element may be embedded in the first flange.